Current methods of determining global ventricular function depend on planar cardiac imaging techniques. In these techniques, activity in front of and behind the heart are superimposed upon left ventricular blood pool activity. In addition, physical constraints prevent images from being acquired along the true long axis of the left ventricle. Recent developments in gated single photon emission computed tomography imaging have shown that it is possible, in approximately the same imaging time, to acquire fully three- dimensional images of the beating heart, and thus of ventricular function. This project set out to determine the accuracy and feasibility of such measurements. It was found that the technique, even when used in a clinically expedient manner (by "reprojection" of the data), produced results that were both more accurate and potentially more reproducible than the existing technique. This finding is expected to have a significant impact on clinical studies (e.g., evaluation of adriamycin therapy) in which clinical decisions are based on small changes in ejection fraction over time. The results have recently been accepted for full publication and will appear in the literature shortly.